Alloy member, apparatus, and method for manufacturing alloy member

ABSTRACT

An alloy member includes a base material that includes a surface layer and is a magnesium-lithium alloy (Mg—Li alloy) having an α-phase and a β-phase, and an anticorrosive film is able to be formed on the surface layer. A degree of orientation in a (110) plane of the β-phase of the Mg—Li alloy is more than or equal to 70%. An average grain size of the Mg—Li alloy is less than or equal to 50 μm. A Li concentration of the surface layer is lower than a Li concentration of inside of the base material.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to an alloy member, an apparatus, and a method for manufacturing an alloy member.

Description of the Related Art

In recent years, a magnesium-lithium alloy (Mg—Li alloy) having a specific gravity smaller than that of a magnesium alloy draws attention. The Mg—Li alloy is lightweight and excellent in vibration damping properties and specific strength, and is expected to be applied to various apparatuses. Lithium, however, is a metal element that is very active and is easily ionized and dissolved. The Mg—Li alloy corrodes more easily than the magnesium alloy that does not include lithium. Japanese Patent Application Laid-Open No. 2013-204127 discusses the process of decreasing the lithium concentration of a surface, serving as a rust-proof coating film, of an Mg—Li alloy and a member thus processed to improve the corrosion resistance of the Mg—Li alloy.

The process discussed in Japanese Patent Application Laid-Open No. 2013-204127, however, is targeted at only a surface layer portion of the Mg—Li alloy, and the corrosion resistance of the member is insufficient.

SUMMARY OF THE INVENTION

According to an aspect of the present disclosure, an alloy member includes a base material that includes a surface layer and is a Mg—Li alloy having an α-phase and a β-phase, wherein an anticorrosive film is able to be formed on the surface layer, wherein a degree of orientation in a (110) plane of the β-phase of the Mg—Li alloy is more than or equal to 70 percent (%), wherein an average grain size of the Mg—Li alloy is less than or equal to 50 micrometres (μm), and wherein a Li concentration of the surface layer is lower than a Li concentration of inside of the base material.

According to another aspect of the present disclosure, a method for manufacturing an alloy member, includes preparing a base material that is molded using die-cast molding and is an Mg—Li alloy having an α-phase and a β-phase, and forming a surface layer on the base material by performing an anodization process on the base material to obtain the surface layer having a Li concentration lower than a Li concentration of inside of the base material.

Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an alloy member according to a first exemplary embodiment.

FIG. 2 is a flowchart illustrating steps of manufacturing an alloy member according to the first exemplary embodiment.

FIG. 3 is a schematic diagram of a die-cast molding apparatus used in a method for manufacturing an alloy member according to the first exemplary embodiment.

FIG. 4 is a schematic diagram of an anodization processing apparatus used in the method for manufacturing the alloy member according to the first exemplary embodiment.

FIG. 5 is a schematic diagram of an imaging apparatus according to a third exemplary embodiment.

FIG. 6 is a schematic diagram of an electronic apparatus according to a fourth exemplary embodiment.

FIG. 7 is a schematic diagram of a moving body according to a fifth exemplary embodiment.

FIG. 8 is a diagram illustrating measurement of a thickness of a surface layer in Example 1.

FIG. 9 is a diagram illustrating measurement of a crystal grain size in Example 1.

FIG. 10 is a schematic diagram of an alloy member according to a second exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS [Alloy Member]

FIG. 1 is a schematic diagram of an alloy member according to a first exemplary embodiment and is a partial enlarged view of a cross section of the alloy member when cut in a lamination direction.

An alloy member 100 is an alloy member in which a base material 101 and an anticorrosive film 103 provided on a surface layer 102 of the base material 101 are laminated together. The application of the alloy member 100 according to the present exemplary embodiment is not particularly limited, and for example, the alloy member 100 can be used as an exterior member, an interior member, and a sliding contact member of an apparatus. In the present disclosure, a form in which the anticorrosive film 103 is not provided is also referred to as an alloy member.

The base material 101 is a magnesium-lithium alloy (Mg—Li alloy) having an α-phase and a β-phase.

In the present exemplary embodiment, the Mg—Li alloy refers to an alloy which contains Mg and Li and in which the sum of a Mg content and a Li content is more than or equal to 90 percent (%) by mass. Using the alloy with a more than or equal to 90% by mass Mg and Li content facilitates weight reduction. The Mg—Li alloy is a lightweight metal material and is more lightweight and more excellent in vibration damping properties and specific strength than an Mg alloy that does not contain Li.

“Excellent in vibration damping properties” means causing vibration to converge fast by quickly converting vibration energy into thermal energy. “Specific strength” is tensile strength per density. The higher the specific strength is, the more likely the alloy member can be made lightweight.

The “α-phase” and the “β-phase” refer to the crystalline phases of the Mg—Li alloy. It is known that the Mg—Li alloy differs in crystal structure according to the amount of the contained Li. The structure is described based on a phase diagram in the literature “‘Nigengokin-jotai-zushu’, written and edited by Seizo Nagasaki and Makoto Hirabayashi, publisher: AGNE Gijutsu Center Inc., ISBN-13: 978-4900041882, release date: 2001/01”. According to this phase diagram, it is understood that in the Mg—Li alloy, a single-phase region of the α-phase, a single-phase region of the β-phase, and a eutectic region simultaneously having the α-phase and the β-phase are present. The α-phase contains a large amount of Mg and is also termed a hexagonal close-packed phase, and the crystal structure of the α-phase is a hexagonal close-packed (hcp) structure. The β-phase contains a large amount of Li and is also termed a body-centered cubic phase, and the crystal structure of the β-phase is a body-centered cubic (bcc) structure. In a case where a Li content is lower than 5% by mass at 25 degrees Celsius (° C.), the Mg—Li alloy only has the α-phase. In a case where a Li content exceeds 11% by mass at 25° C., the Mg—Li alloy only has the β-phase. The Mg—Li alloy having the α-phase and the β-phase at 25° C. is the alloy having a Li content of more than or equal to 5% by mass and less than or equal to 11% by mass. The crystal structure of the Mg—Li alloy can be identified by an X-ray diffraction measurement such as a 2θ/θ measurement.

The presence of the α-phase can be verified by identifying the indices of the planes of a hexagonal crystal based on powder X-ray diffraction data on a Li0.18-Mg0.82 alloy (National Research and Development Agency, National Institute for Materials Science, inorganic materials database), for example. The presence of the β-phase can be verified by identifying the indices of the planes of a body-centered cubic crystal based on powder X-ray diffraction data on a Li0.5-Mg0.5 alloy (National Research and Development Agency, National Institute for Materials Science, inorganic materials database), for example.

The degree of orientation in a (110) plane of the β-phase of the Mg—Li alloy is more than or equal to 70%. The (110) plane of the β-phase is a close-packed plane of the β-phase. The degree of orientation in the (110) plane of the β-phase, which is an inert crystal plane, is high, namely more than or equal to 70%, whereby it is possible to reduce the starting points of corrosion of the base material 101. Thus, the alloy member according to the present disclosure is excellent in corrosion resistance. The degree of orientation in the (110) plane of the β-phase can be measured by the following method.

The degree of orientation in the (110) plane of the β-phase is obtained as follows. First, in the range where 2θ is more than or equal to 20 degrees (°) and less than or equal to 100°, a diffraction pattern is acquired by the 2θ-θ measurement, and the background is removed from the acquired diffraction pattern. Next, with respect to the peaks of the diffraction pattern from which the background is removed, the indices of the planes of a body-centered cubic crystal are identified based on the powder X-ray diffraction data on the Li0.5-Mg0.5 alloy. Each of the intensities of X-ray diffraction corresponding to the identified plane indices of the body-centered cubic crystal is divided by the intensity ratio of a corresponding powder X-ray, and the resulting values are totaled. A value obtained by dividing each of the X-ray intensities of the plane indices of a (110) plane and a (220) plane equivalent to close-packed planes of the body-centered cubic crystal by the intensity ratio of a corresponding powder X-ray is divided by the above total value.

The average grain size of the Mg—Li alloy is less than or equal to 50 micrometers (μm). Because the average grain size is less than or equal to 50 μm, it is easy to thickly form the surface layer 102 of the alloy member 100 according to the present disclosure. This average grain size is suitable also in terms of an increase in the corrosion resistance of the base material 101. The average grain size can be controlled to be in a desired range by adjusting the injection speed and the cooling speed of die-cast molding. The faster the injection speed and the cooling speed are, the smaller the grain size can be. The crystal shape of the α-phase of the Mg—Li alloy is a needle shape. The “needle shape” refers to a crystal having the aspect ratio, i.e., the ratio of the length of the major axis to the length of the minor axis, of 4 or more. It is desirable that the average grain size of the α-phase should be less than or equal to 30 μm. The α-phase is a crystalline phase in which Li is less likely to move when an anodization process is performed. If the grain size of the crystal of the α-phase is great, it is difficult to perform the anodization process at a small voltage or in a short time. If, however, the average grain size of the α-phase is less than or equal to 30 μm, Li is efficiently incorporated into the anticorrosive film 103 when the anodization process is performed. It is thus possible to form the surface layer 102 at a relatively small voltage or in a relatively short time. In terms of an increase in the corrosion resistance of the base material 101, it is also desirable that the average grain size should be less than or equal to 30 μm.

The Mg—Li alloy may also contain another metal element to adjust its properties as long as the amount of the contained metal element is less than or equal to 10% by mass. Specifically, the Mg—Li alloy may contain one or more elements selected from a first group consisting of aluminum (Al), zinc (Zn), manganese (Mn), silicon (Si), calcium (Ca), germanium (Ge), and beryllium (Be).

For example, it is desirable that the Mg—Li alloy should have an Al content of less than or equal to 10% by mass. In terms of an increase in the strength of the base material 101, it is desirable that the Mg—Li alloy should have an Al content of more than or equal to 1% by mass and less than or equal to 10% by mass.

Zn, Mn, Si, and Ca can increase the strength of the base material 101. As for Zn, it is desirable that the Mg—Li alloy should have a Zn content of less than or equal to 3% by mass. It is more desirable that the Mg—Li alloy should have a Zn content of more than or equal to 0.2% by mass and less than or equal to 3% by mass. As for Mn, it is desirable that the Mg—Li alloy should have a Mn content of less than or equal to 0.3% by mass. It is more desirable that the Mg—Li alloy should have a Mn content of more than or equal to 0.1% by mass and less than or equal to 0.3% by mass. As for Si, it is desirable that the Mg—Li alloy should have a Si content of less than or equal to 0.2% by mass. It is more desirable that the Mg—Li alloy should have a Si content of more than or equal to 0.1% by mass and less than or equal to 0.2% by mass. As for Ca, it is desirable that the Mg—Li alloy should have a Ca content of less than or equal to 1.0% by mass. It is more desirable that the Mg—Li alloy should have a Ca content of more than or equal to 0.1% by mass and less than or equal to 1.0% by mass.

Ge and Be miniaturize the crystal of the Mg—Li alloy and increase the corrosion resistance of the base material 101.

As for Ge, it is desirable that the Mg—Li alloy should have a Ge content of less than or equal to 1% by mass. It is more desirable that the Mg—Li alloy should have a Ge content of more than or equal to 0.1% by mass and less than or equal to 1% by mass. As for Be, it is desirable that the Mg—Li alloy should have a Be content of less than or equal to 3% by mass. It is more desirable that the Mg—Li alloy should have a Be content of more than or equal to 0.04% by mass and less than or equal to 3% by mass.

The shape of the base material 101 is not particularly limited. The shape of the base material 101 is not limited to a hexahedron, such as a cuboid or a cube, and may be a cylinder, a sphere, a prism, a cone, or a tube.

The surface layer 102 is a portion formed on a surface of the base material 101. The Li concentration of the surface layer 102 is lower than the Li concentration of the inside of the base material 101, which is a portion other than the surface layer 102. In other words, the Mg concentration of the surface layer 102 is higher than the Mg concentration of the inside of the base material 101. The “surface layer 102” not only refers to a portion of the base material 101 on the side where the anticorrosive film 103 is provided, but also includes the surfaces on the bottom surface and the side surfaces of the base material 101. That is, the surface layer 102 may be formed on the left and right sides or the lower side of the base material 101 on the plane of the paper in FIG. 1 . Since the Li concentration of the surface layer 102 is lower than that of the inside of the base material 101, the surface layer 102 is less likely to corrode than the inside of the base material 101. The alloy member 100 includes the surface layer 102, whereby the inside of the base material 101 is less likely to corrode even if the anticorrosive film 103 deteriorates. Thus, the durability of the alloy member 100 as a member improves. The greater the thickness (the length in the lamination direction) of the surface layer 102 is, the less likely the inside of the base material 101 is to corrode. It is desirable that the thickness of the surface layer 102 should be more than or equal to 10 μm. In terms of the prevention of the deposition of lithium, it is more desirable that the thickness of the surface layer 102 should be more than or equal to 30 μm. If, on the other hand, the thickness of the surface layer 102 is too great, the manufacturing process takes longer time, or a power supply capable of applying a high voltage is required. Thus, it is desirable that the thickness of the surface layer 102 should be less than or equal to 100 μm. In the surface layer 102, a Li compound is less likely to be deposited than in the base material 101. Specifically, when the alloy member 100 is cut as illustrated in FIG. 1 and four hours elapse, the deposition amount of the Li compound is smaller in the surface layer 102 than in the base material 101. On the other hand, since the Li concentration of the base material 101 is higher than that of the surface layer 102, surplus lithium is more likely to be deposited as lithium carbonate (Li₂CO₃) or lithium oxide (Li₂O) in the base material 101 than in the surface layer 102. Since the Li compound can be the starting points of corrosion, a more desirable form is a form in which the Li compound is not deposited on the surface layer 102 even if the alloy member 100 is cut. The surface layer 102 can be formed by, for example, the step of reforming the surface of the base material 101 by an anodization process and forming the anticorrosive film 103. The method for measuring whether the Li concentration of the surface layer 102 is lower than the Li concentration of the inside of the base material 101 is not particularly limited.

The Li concentration may be measured by X-ray photoelectron spectroscopy (XPS) while the alloy member 100 is polished in the thickness direction, or the Li concentration may be guessed by measuring the Mg concentration by energy-dispersive X-ray spectroscopy using a scanning electron microscope (SEM-EDX).

The anticorrosive film 103 can be formed on the surface layer 102. In FIG. 1 , the anticorrosive film 103 is formed on the surface layer 102. The anticorrosive film 103 is a film formed for the purpose of avoiding exposure of the surface (the surface layer 102) of the base material 101 to atmospheric air. The anticorrosive film 103 prevents lithium on the surface of the base material 101 from reacting with moisture in atmospheric air. The anticorrosive film 103 is a film composed of an inorganic compound including an inorganic fluoride. Examples of the inorganic fluoride include magnesium fluoride (MgF₂). The main component of the inorganic fluoride of the anticorrosive film 103 is MgF₂, and the proportion of the MgF₂ is more than or equal to 90% by volume. Since the main component of the inorganic fluoride of the anticorrosive film 103 is MgF₂, it is possible to prevent corrosion of the base material 101. This is because MgF₂ has the property of being insensitive to moisture.

The inorganic fluoride of the anticorrosive film 103 may also include lithium fluoride (LiF) and/or an oxide in addition to the MgF₂ as long as the proportion of the LiF and/or the oxide is less than or equal to 10% by volume. The volume proportion of the MgF₂ in the inorganic fluoride of the anticorrosive film 103 can be calculated, for example, based on the 2θ/θ measurement of the X-ray diffraction measurement. It is desirable that the thickness (the length in the lamination direction) of the anticorrosive film 103 should be more than or equal to 2 μm. With the thickness, it is possible to sufficiently block water or moisture in the air over the surface layer 102. It is more desirable that the thickness of the anticorrosive film 103 should be more than or equal to 5 μm. It is even more desirable that the thickness of the anticorrosive film 103 should be more than or equal to 20 The anticorrosive film 103 can be formed by the same step as the step of reforming the surface of the base material 101 to form the surface layer 102 by the anodization process.

In the alloy member 100, the anticorrosive film 103 may not be exposed. For example, a coating film, such as a primer or a topcoat layer, may further be provided on the anticorrosive film 103 according to the user's purpose. Examples of the coating film include a thermal barrier film having a thermal barrier function. Examples of the material of the coating film include a cured product of a curable resin. Examples of the curable resin include a thermosetting resin and a photocurable resin.

As described above, in the alloy member according to the present exemplary embodiment, the Li concentration of the surface layer 102 of the base material 101 which is an Mg—Li alloy having more than or equal to 70% of the degree of orientation in the (110) plane of a β-phase and less than or equal to 50 μm of the average grain size is lower than the Li concentration of the inside of the base material 101. The base material 101 is excellent in corrosion resistance, and the surface layer 102 having a low Li concentration is provided on the base material 110. Thus, the alloy member according to the present disclosure is more excellent in corrosion resistance than a conventionally known alloy member in which the Li concentration of a surface layer of a base material is merely lower than the Li concentration of the inside of the base material.

[Method for Manufacturing Alloy Member]

Next, with reference to FIGS. 2, 3, and 4 , a method for manufacturing the alloy member according to the present disclosure is described.

FIG. 2 is a flowchart illustrating steps of manufacturing the alloy member. FIG. 3 is a schematic diagram of a die-cast molding apparatus that performs die-cast molding. FIG. 4 is a schematic diagram of an anodization apparatus that performs an anodization process.

The method for manufacturing the alloy member according to the present disclosure includes a preparing step of preparing a base material by die-cast molding to obtain an Mg—Li alloy having an α-phase and a β-phase, and a forming step of forming a surface layer on the base material by performing an anodization process on the base material to obtain a surface layer having a Li concentration lower than that of the inside of the base material.

First, the preparing step is described. In the preparing step, a base material is prepared by die-cast molding to obtain an Mg—Li alloy having an α-phase and a β-phase. The die-cast molding refers to a molding method in which a metal as a raw material is melted at high temperature and the molten metal is forced into a mold under application of pressure. The die-cast molding is different from casting in that the die-cast molding involves application of pressure when the molten metal is forced into a cavity of a mold and the casting does not involve application of pressure.

The procedure of the die-cast molding is described as an example of the preparing step.

First, in step S11, a cylindrical billet 201 as an Mg—Li alloy that is an alloy raw material as a raw material of a base material is prepared. The method for obtaining the cylindrical billet 201 is not particularly limited. The cylindrical billet 201 may be cut out of a material obtained by a molding step, such as casting, Thixomolding, forging molding, or extrusion molding. The shape of the billet is not limited to a cylinder.

Next, in step S12, the cylindrical billet 201 is melted, and the base material 101 is obtained by the die-cast molding. A die-cast molding apparatus 200 illustrated in FIG. 3 includes a melting tank 202, an injection cylinder 203, a plunger 204, and a metal mold 205. The melting tank 202 is connected to the injection cylinder 203 by piping (not illustrated). The cylindrical billet 201 is melted by being heated in the melting tank 202. The melting temperature is more than or equal to 600° C., for example. The molten alloy raw material passes through the piping, flows into the injection cylinder 203, and is poured into the metal mold 205 at a desired injection speed by the plunger 204 applying pressure to the molten alloy raw material. The desired speed is in the range of more than or equal to 1000 cubic centimeters per seconds (cm3/seconds) and less than or equal to 20000 cm3/seconds, for example. The melted alloy raw material is cooled at a speed faster than the casting and solidified in the metal mold 205, whereby the base material 101 is obtained. The cooling speed of general casting is in the range of more than or equal to 1° C./seconds and less than or equal to 5° C./seconds. It is desirable that the cooling should be quenching. The speed of the quenching is in the range of more than or equal to 100° C./seconds and less than or equal to 800° C./seconds, for example. In the base material 101 obtained by the die-cast molding, the degree of orientation in the (110) plane of the β-phase of the Mg—Li alloy is more than or equal to 70%, and the average grain size of the Mg—Li alloy is less than or equal to 50 μm.

Next, in step S13, the base material 101 is heat-treated by a heat treatment (a heat treatment step). In the base material 101 which is the Mg—Li alloy obtained by the die-cast molding, concentration unevenness may occur in which the lithium concentration differs depending on the portion of the base material 101. The concentration unevenness, however, can be decreased by the heat treatment. It is desirable that the temperature of the heat treatment should be in the range of more than or equal to 100° C. and less than or equal to 320° C. In this range, the deformation of the base material 101 is small, and the concentration unevenness can be reduced. If the heat treatment is performed at a temperature above 320° C., the deformation of the base material 101 may be great. If the Mg—Li alloy includes Al, the Al and the Li may form a compound. If the compound of the Al and the Li is formed, the compound may act as resistance when the anodization process is performed, and the Li concentration of the surface layer 102 may not be able to be sufficiently reduced. It is more desirable that the temperature of the heat treatment should be more than or equal to 100° C. and less than or equal to 180° C. In terms of an increase in the dimensional accuracy of the base material 101, however, the heat treatment may not necessarily be performed.

Next, the forming step is described. First, in step S14, the base material 101 is washed. The washing involves, for example, degreasing, water washing, or etching, to remove a release agent, an oxide layer, and a segregation substance on the surface of the base material 101 by. Examples of the washing method include the following. A conduction holding jig 308 of the same material as the base material 101 is connected to the base material 101. Specifically, the conduction holding jig 308 is bent and connected to the base material 101 by holding the base material 101. The base material 101 and the conduction holding jig 308 are immersed in nitric acid (a concentration of 3 to 5% by mass) and acid-washed, whereby the oxide layer is removed. The acid may be hydrochloric acid or sulfuric acid instead of the nitric acid, and is not particularly limited as far as the oxide layer on the surface is dissolved. After the acid washing, the base material 101 and the conduction holding jig 308 are water-washed using pure water. Then, the base material 101 and the conduction holding jig 308 are immersed in pure water heated to the range of more than or equal to 90° C. and less than or equal to 99° C., taken out from the water, and dried.

An anodization apparatus 309 illustrated in FIG. 4 includes a treatment tank 301 that stores an electrolyte solution 302. The anodization apparatus 309 also includes a pump 303 and a filter 304 that circulate and agitate the electrolyte solution 302 from a lower portion to an upper portion of the treatment tank 301 through piping. The anodization apparatus 309 also includes a power supply 305. The cathode of the power supply 305 is electrically connected to a cathode electrode 306, which is a base material immersed in the electrolyte solution 302 in the treatment tank 301. The material of the cathode electrode 306 is not particular limited as long as the material has low reactivity with the electrolyte solution 302, and for example, carbon, platinum, titanium, or stainless steel (SUS) can also be used. The anode of the power supply 305 is connected to the conduction holding jig 308 connected to the base material 101, and thus, the base material 101 and the conduction holding jig 308 function as an anode electrode.

In the forming step, first, in step S15, the base material as the cathode and the base material 101 as the anode are placed in a neutral ammonium fluoride aqueous solution (a placement step). In the treatment tank 301, the neutral ammonium fluoride aqueous solution is stored as the electrolyte solution 302. It is desirable that the concentration of the neutral ammonium fluoride aqueous solution should be from 200 g/L to a saturated solution. It is desirable that the concentration of the neutral ammonium fluoride aqueous solution should be high to fluoridate a large portion of the surface of the base material 101. It is desirable that the aqueous solution of the electrolyte solution 302 should be neutral, and the pH of the aqueous solution should be more than or equal to 6.0 and less than or equal to 8.0. If the pH decreases and the aqueous solution becomes acidic, hydrogen fluoride is generated. If, on the other hand, the pH increases and the aqueous solution becomes alkaline, oxidation reaction at the anode occurs not only with fluorine but also with oxygen. Thus, the proportion of fluorine contained in the anticorrosive film 103 decreases. It is more desirable that the value of the pH should be in the range of 7.0 to 7.5. If the pH is in this range, it is easy to apply a higher voltage. Thus, it is easy to thickly form the anticorrosive film 103. The temperature of the electrolyte solution 302 rises by the pump 303. It is desirable that the temperature of the electrolyte solution 302 should be controlled by a chiller. It is desirable that the temperature of the electrolyte solution 302 should be from −20° C. to 60° C. The liquid may be agitated using bubbling agitation in combination. A filter may be provided to filter lithium fluoride (LiF) generated in the liquid.

When the anode electrode (the base material 101 and the conduction holding jig 308) and the cathode electrode 306 (a voltage application step) are connected to the power supply 305, then in step S16, a voltage is applied between the anode electrode and the cathode electrode 306. When the voltage is applied, a fluoride film which is the anticorrosive film 103 including an inorganic fluoride, i.e., MgF₂, as the main component starts to be formed. After continuous application of the voltage, Li that is included in the β-phase of the Mg—Li alloy and present near the surface of the base material 101 is incorporated into the anticorrosive film 103. The Li is incorporated, whereby the surface layer 102 having a Li concentration lower than that of the inside of the base material 101 starts to be formed. As a result, the application of the voltage forms the anticorrosive film 103 and also forms the surface layer 102. Since the base material 101 according to the present disclosure is die-cast molded, the average grain size of the Mg—Li alloy is sufficiently small, namely less than or equal to 50 Thus, even if the α-phase, in which Li is less likely to be incorporated into the anticorrosive film 103 even by applying a voltage, is present, it is possible to easily and thickly form the surface layer 102 having a Li concentration lower than that of the inside of the base material 101. It is possible to increase the thickness of the surface layer 102 by applying a high voltage. More specifically, the setting current value is increased and the liquid concentration is decreased, which allows application of a higher voltage, and consequently, leads to increase in the thickness of the surface layer 102. Further, it is possible to further increase the thickness of the surface layer 102 by increasing the temperature of the electrolyte solution 302. If, however, the temperature is excessively raised, hydrofluoric acid may be produced from the electrolyte. Thus, it is desirable that the temperature of the electrolyte solution 302 should be less than or equal to 55° C. The thickness of the anticorrosive film 103 is proportional to the total amount of current (the coulomb amount) flowing through a unit area of the base material 101. It is desirable to apply a current under the condition of more than or equal to 100 coulombs per 10 cm2. This can realize formation of an anticorrosive film having sufficient thickness and excellent in corrosion resistance.

Then, the base material 101 and the conduction holding jig 308 are water-washed and dried, and the conduction holding jig 308 is detached from the base material 101, whereby the alloy member 100 in which the anticorrosive film 103 including MgF₂ as an inorganic fluoride and the surface layer 102 are formed can be obtained.

As described above, since the base material of the alloy member obtained by the manufacturing method according to the present disclosure is die-cast molded, the degree of orientation in the (110) plane of the β-phase is more than or equal to 70%, and the average grain size of the base material is less than or equal to 50 Thus, the base material is excellent in corrosion resistance. Since the anodization process is performed on the die-cast molded base material, it is easy to thickly form a surface layer having a Li concentration lower than in the conventional art. Thus, based on the manufacturing method according to the present disclosure, it is possible to provide the alloy member more excellent in corrosion resistance than a conventionally known alloy member in which the Li concentration of a surface layer of a base material is merely lower than the Li concentration of the inside of the base material.

[Alloy Member]

FIG. 10 is a schematic diagram of an alloy member according to a second exemplary embodiment and is a partial enlarged view of a cross section of the alloy member when cut in the lamination direction. The alloy member according to the second exemplary embodiment is different from the alloy member according to the first exemplary embodiment in that the alloy member according to the second exemplary embodiment includes a coating film on an anticorrosive film. The differences from the first exemplary embodiment are mainly described below.

An alloy member 1000 is an alloy member in which a base material 1001, an anticorrosive film 1003 formed on a surface layer 1002 of the base material 1001, and a coating film 1004 provided on the anticorrosive film 1003 are laminated together. The coating film 1004 includes a cured product of a resin. The coating film 1004 may be a single layer or a plurality of layers. For example, a primer layer may be provided on the anticorrosive film 1003, and the cured product of the resin may be formed on the primer layer. The type of the resin is not particularly limited, and a thermosetting resin or a photocurable resin can be used.

The base material 1001 is a magnesium-lithium alloy (Mg—Li alloy) having an α-phase 1006 and a β-phase 1007.

The anticorrosive film 1003 includes a plurality of pores 1005 inside and on its surface. That is, the anticorrosive film 1003 has a porous structure. In the present exemplary embodiment, a pore means a portion where a gap having an average circle equivalent diameter of more than or equal to 0.1 μm is recognized in a case where the portion is observed with an electron microscope. An uncured resin as a precursor of the coating film 1004 is provided on the anticorrosive film 1003, and the uncured resin is cured in the state where the resin is injected into the pores 1005 and the pores 1005 are filled with the resin. This causes an anchor effect and improves the adhesiveness between the anticorrosive film 1003 and the coating film 1004. In terms of improvement in the adhesiveness, it is desirable that the number of the pores 1005 should be more than or equal to 10, and the average circle equivalent diameter of the pores 1005 should be in the range of a diameter of more than or equal to 0.1 μm and a diameter of less than or equal to 1 μm in a region of 20 μm×20 μm in the anticorrosive film 1003.

The anticorrosive film 1003 is thickly formed on the β-phase 1007 of the base material 1001 and thinly formed on the α-phase 1006. This forms a great difference in level that is not caused by pores on a surface of the surface layer 1002 in contact with the anticorrosive film 1003. It is desirable that an average surface roughness Ra of a surface of the anticorrosive film 1003 in contact with the coating film 1004 (a surface on the opposite side of a surface of the anticorrosive film 1003 in contact with the surface layer 1002) should be in the range of more than or equal to 0.19 μm and less than or equal to 0.9 μm. When the average surface roughness Ra is in this range, the adhesiveness is excellent, and the external appearance is also excellent. If the average surface roughness Ra is less than 0.19 μm, the adhesive force may be insufficient, and the coating film 1004 may be likely to peel off. If the average surface roughness Ra exceeds 0.9 μm, the unevenness of the anticorrosive film 1003 may affect the coating film 1004, and the external appearance may be impaired.

It is desirable that a maximum roughness Rz of the surface of the anticorrosive film 1003 in contact with the coating film 1004 should be less than or equal to 15 μm. When the maximum roughness Rz is in this range, the adhesiveness is excellent, and the external appearance is also excellent. It is more desirable that the maximum roughness Rz should be in the range of more than or equal to 1 μm and less than or equal to 15 If the maximum roughness Rz exceeds 15 μm, the roughness (unevenness) of the anticorrosive film 1003 may affect the coating film 1004, and the external appearance may be impaired.

The average surface roughness Ra, the maximum roughness Rz, and the density and the sizes of the pores can be adjusted according to the conditions for the anodization process. For example, if the coulomb amount in the anodization process is increased, the average surface roughness Ra increases. Moreover, if the coulomb amount in the anodization process is increased, the maximum roughness Rz increases.

[Optical Apparatus and Imaging Apparatus]

FIG. 5 illustrates the configuration of a single-lens reflex digital camera 600, which is an imaging apparatus as an example of an apparatus according to a third exemplary embodiment of the present disclosure. In FIG. 5 , a camera main body 602 and a lens barrel 601 as an optical apparatus are joined together. The lens barrel 601 is an interchangeable lens which is attachable to and detachable from the camera main body 602.

Light from an object passes through an optical system including a plurality of lenses 603 and 605 as examples of components placed on an optical axis of an imaging optical system in a housing 620 of the lens barrel 601 and is received by an image sensor 610, whereby an image is captured. The lens 605 is supported by an inner barrel 604 and movable relative to an outer barrel of the lens barrel 601 in focusing or zooming.

During an observation period before image capturing, light from an object is reflected by a main mirror 607 as an example of a component in a housing 621 of the camera main body 602 and passes through a prism 611, and then, a captured image is displayed through a viewfinder lens 612 to a user. For example, the main mirror 607 is a one-way mirror, and light having passed through the main mirror 607 is reflected in the direction of an autofocus (AF) unit 613 by a sub-mirror 608. For example, this reflected light is used for distance measurement. The main mirror 607 is attached to and supported by a main mirror holder 640 by bonding. The main mirror 607 and the sub-mirror 608 are moved to outside the optical path via a driving mechanism (not illustrated) when image capturing is performed, a shutter 609 is opened, and an optical image to be captured that is incident from the lens barrel 601 is formed on the image sensor 610. A diaphragm 606 is configured to change brightness and the depth of focus in the image capturing by changing the opening area of the diaphragm 606.

The alloy member according to the present exemplary embodiments can be used in at least parts of the housings 620 and 621. The housings 620 and 621 may include only an Mg—Li alloy member, or a coating film may be provided on the alloy member according to the present exemplary embodiments. Since the Mg—Li alloy according to the present disclosure is excellent in corrosion resistance, it is possible to provide an imaging apparatus more excellent in corrosion resistance than a conventional imaging apparatus.

Although the imaging apparatus has been described using the single-lens reflex digital camera as an example, the present disclosure is not limited to this, and may be employed in a smartphone or a compact digital camera.

[Electronic Apparatus]

FIG. 6 illustrates the configuration of a personal computer, which is an electronic apparatus as an example of an apparatus according to a fourth exemplary embodiment of the present disclosure. In FIG. 6 , a personal computer 800 includes a display unit 801 and a main body unit 802. Inside a housing 820 of the main body unit 802, an electronic component 803 as an example of a component provided in the housing 820 is included. The alloy member according to the present exemplary embodiments can be used in at least a part of the housing 820 of the main body unit 802. The housing 820 may include only an Mg—Li alloy member, or a coating film may be provided on the alloy member according to the present exemplary embodiments. Since the Mg—Li alloy according to the present disclosure is excellent in corrosion resistance, it is possible to provide a personal computer more lightweight and more excellent in corrosion resistance than a conventional personal computer.

Although the electronic apparatus has been described using the personal computer 800 as an example, the present disclosure is not limited to this, and may be employed in a smartphone or a tablet.

[Moving Body]

FIG. 7 illustrates a drone as an example of a moving body according to a fifth exemplary embodiment of the present disclosure. A drone 700 includes a plurality of driving units 701 and a main body unit 702 connected to the driving units 701. In the main body unit 702, a driving circuit 705 as an example of a component is provided. The driving units 701 include, for example, propellers. As illustrated in FIG. 7 , leg portions 703 are connected to the main body unit 702, and a camera 704 is connected to the main body unit 702. The alloy member according to the present exemplary embodiments can be used in at least part of a housing 710 of the main body unit 702 and the leg portions 703. The housing 710 may include only an Mg—Li alloy member, or a coating film may be provided on the alloy member according to the present exemplary embodiments. Since the Mg—Li alloy according to the present disclosure is excellent in corrosion resistance, it is possible to provide a drone more excellent in vibration damping properties and corrosion resistance than a conventional drone.

Although the moving body has been described using the drone 700 as an example, the present disclosure is not limited to this, and may be employed in an automobile or an aircraft.

EXAMPLES

The present disclosure is described more specifically below taking Examples. The present disclosure, however, is not limited to the following examples.

[Method for Manufacturing Alloy Member] Example 1

First, a cylindrical billet of an Mg—Li alloy as an alloy raw material was prepared. The Mg—Li alloy was Ares (composition: Mg-9% Li-1% Zn-4% Al, manufactured by Amli Materials Technology Co., Ltd.). As the sizes of the cylinder, the diameter of the bottom surface of the cylinder was 90 millimeters (mm), and the length of the cylinder was 300 mm. Using the die-cast molding apparatus 200 illustrated in FIG. 3 , the cylindrical billet was melted at 610° C., and the molten alloy raw material was forced into the metal mold 205 at an injection speed of 5000 cm³/seconds. The temperature of the metal mold 205 was 150° C., and the molten alloy raw material was solidified at a cooling speed of 500° C./seconds, whereby a die-cast molded base material was obtained. The shape of the obtained base material was a circular ring shape having a diameter of 110 mm, a thickness of 2.0 mm, and a volume of 40 cm³.

Next, using the anodization apparatus 309 illustrated in FIG. 3 , a surface layer and an anticorrosive film were formed. Specifically, the base material was connected to the conduction holding jig 308 prepared using Ares to form an anode electrode using the base material of the circular ring shape and the conduction holding jig 308. The cathode electrode 306 was made of carbon. The electrolyte solution 302 was a neutral ammonium fluoride aqueous solution (pH=7.0) having a concentration of 230 grams per liter (g/L). The cathode electrode 306 and the anode electrode were placed in the neutral ammonium fluoride aqueous solution. Next, a voltage was applied between the cathode electrode 306 and the anode electrode. The temperature of the electrolyte solution 302 was controlled to be 50° C.±2° C. The current value of the power supply 305 was set to 20 amperes (A), the integral value of the current (the coulomb amount) after the voltage was applied was monitored, and the coulomb amount per unit area was controlled to be 400 coulombs (C) to maintain the coulomb amount to be the same under all conditions. An alloy member in Example 1 was obtained by the above steps.

Example 2

Example 2 is different from Example 1 in the temperature of the electrolyte solution 302. In example 2, the temperature of the electrolyte solution 302 was controlled to be 30° C.±2° C. An alloy member in Example 2 was obtained by steps similar to those in Example 1 except for the difference in temperature.

Example 3

Example 3 is different from Example 1 in the temperature of the electrolyte solution 302. In Example 3, the temperature of the electrolyte solution 302 was controlled to be 20° C.±2° C. An alloy member in Example 3 was obtained by steps similar to those in Example 1 except for the difference in temperature.

Example 4

Example 4 is different from Example 1 in that heat treatment was performed before the anodization process. In Example 4, the base material was placed in an atmosphere furnace heated to 180° C., and the base material was heat-treated for an hour. An alloy member in Example 4 was obtained by steps similar to those in example 1 except for the difference in heat treatment.

Example 5

Example 5 is different from Example 1 in that heat treatment was performed before the anodization process. In Example 5, the base material was placed in an atmosphere furnace heated to 320° C., and the base material was heat-treated for an hour. An alloy member in Example 5 was obtained by steps similar to those in Example 1 except for the difference in heat treatment.

Comparative Example 1

Comparative example 1 is different from Example 1 in the step of preparing a base material. In Comparative example 1, a cylindrical billet formed by casting and having a diameter of 500 mm was subjected to cutting to obtain a base material of a circular ring shape having a diameter of 110 mm, a thickness of 1.5 mm, and a volume of 150 cm³. The casting was performed by injecting a molten metal into a metal mold without applying pressure, and then cooling the metal under the condition of a cooling speed of 5° C./seconds. An alloy member in Comparative example 1 was obtained by steps similar to those in example 1 except for the difference in preparing.

[Evaluation of Alloy Member]

Next, evaluation methods performed on Examples 1 to 5 and Comparative example 1 and the results of the evaluation are described.

(Measurement of Thickness of Surface Layer)

The thickness of the surface layer was measured using a scanning electron microscope (SEM) (Sigma 500 VP manufactured by Carl Zeiss Microscopy Co., Ltd.). The measurement was made under the conditions of a voltage of 5 kilovolts (kV), a working distance of 7.0 mm, and an aperture size of 60 μm. First, in the field of view at a magnification of 500 times (570×420 μm), the neighborhood of the boundary between the anticorrosive film and the base material was selected, and the thickness of the surface layer was measured. A measurement sample was obtained by the following method. First, a resin-embedded sample in each example was prepared, cut, then wet-polished and buffing-polished, and then dry-polished by ion milling. Then, after the lapse of two hours from the dry polishing, the sample was observed.

FIG. 8 is an image of the cross section of the alloy member in Example 1. The alloy member includes a Li compound 402, which is lithium carbonate.

The size of the lithium carbonate was about 1 μm. The alloy member in FIG. 8 has a region where the Li compound 402 is deposited and a region where a Li compound is not deposited. A composition analysis was performed on these regions by SEM-EDX, and a region having a high Mg concentration was determined as the surface layer 102. A dashed line in FIG. 8 indicates a boundary line L1 between these regions. A dashed-dotted line in FIG. 8 indicates a boundary line L2 between the anticorrosive film 103 and the region where a Li compound is not deposited. A distance t1 from the boundary line L1 to the boundary line L2 was determined as the thickness of the surface layer 102. The distance t1 was obtained by measuring the distances at three places in a single field of view and the average value of the distances is obtained.

(Measurement of Crystal Grain Size)

The crystal grain size of the Mg—Li alloy was measured using a scanning electron microscope (SEM) (Sigma 500 VP manufactured by Carl Zeiss Microscopy Co., Ltd.). First, in the field of view at a magnification of 200 times (550×400 μm), a position near an interface was selected. Next, in the field of view at a magnification of 2000 times (55×40 μm), the crystal grain size was measured. A measurement sample was the sample used to measure the thickness of the surface layer.

FIG. 9 is an image of the cross section of the alloy member in Example 1 at a magnification of 2000 times. An α-phase 501 having a needle shape is surrounded by a β-phase 502. Regarding the grain size, the maximum length of the α-phase 501 was measured and defined as the crystal grain size. In a case where the β-phase 502 was surrounded by the α-phase 501, the maximum length of the β-phase 502 was defined as the crystal grain size. The crystal grain sizes at three places in a single field of view were measured, and the average value of the crystal grain sizes was obtained.

(Measurement of Crystalline Orientation)

The degree of orientation in the (110) plane of the β-phase was measured by the X-ray diffraction method. Ultima IV manufactured by Rigaku Corporation was used as an X-ray diffraction apparatus. A Cu tubular lamp was used as a tubular lamp, and a measurement wavelength λ was 1.5418 angstrom (A). The tube voltage was 40 kV, and the tube current was 40 milliamperes (mA).

First, in the range where 2θ is more than or equal to 20° and less than or equal to 100° or less, a diffraction pattern was acquired by the 2θ-θ method. The step width was 0.02°, and the speed was 2°/min (integrated twice).

The background was removed from the acquired diffraction pattern.

Next, with respect to the peaks of the diffraction pattern from which the background was removed, the indices of the planes of a body-centered cubic crystal were identified based on the powder X-ray diffraction data on the Li0.5-Mg0.5 alloy.

Each of the intensities of X-ray diffraction corresponding to the identified plane indices of the body-centered cubic crystal was divided by the intensity ratio of a corresponding powder X-ray, and the resulting values were totaled. Then, a value obtained by dividing each of the X-ray intensities of the plane indices of a (110) plane and a (220) plane of the body-centered cubic crystal by the intensity ratio of a corresponding powder X-ray was divided by the above total value, to calculate the degree of orientation in the (110) plane of the β-phase.

The measurement planes were subjected to #2000 finishing polishing by a polishing machine.

(Evaluation of Durability)

The durability was evaluated by a weight reduction test. The weight of a measurement sample was measured before the measurement sample was immersed in a nitric acid aqueous solution having a pH of 1.5 and after the measurement sample was immersed in the nitric acid aqueous solution for three hours. That the weight reduction rate is small means that durability in long-term use is excellent. A product having a weight reduction rate of less than or equal to 1% was ranked A, a product having a weight reduction rate in the range of more than or equal to 1% and less than or equal to 2.5% was ranked B, and a product having a weight reduction rate of more than or equal to 2.5% was ranked C. Then, the products ranked A and B were determined as non-defective products.

The results of the above measurements and evaluations are summarized in table 1.

TABLE 1 Liquid Thickness Temperature temperature Grain Degree of of surface of heat of size orientation layer treatment electrolyte μm % μm ° C. ° C. Durability - Example 1 25 74.4 40 absent 50 A Example 2 18 74.1 30 absent 30 A Example 3 24 74.3 20 absent 20 B Example 4 40 72.6 30 180 50 A Example 5 47 75.2 10 320 50 B Comparative 120 41.5 0 absent 50 C example 1

From the results in table 1, all of the alloy members in Examples 1 to 5, in which the average grain size was less than or equal to 50 μm and the degree of orientation in the (110) plane of the β-phase was more than or equal to 70%, have the surface layer of 10 μm or more and excellent durability. On the other hand, Comparative example 1, in which the average grain size was greater than 50 μm and the degree of orientation in the (110) plane of the β-phase was less than 70%, the durability was poor.

Among Examples 1 to 3, the higher the liquid temperature of the electrolyte was, the greater the thickness of the surface layer was. From this result, it is understood that the higher the liquid temperature is, the more easily Li can be moved from the surface of the base material.

Among Examples 1, 4, and 5, the higher the temperature of the heat treatment was, the greater the crystal grain size was, and the smaller the thickness of the surface layer was. Among examples 4 and 5 in which the crystal grain size was greater than in Example 1, the α-phase was connected in a ring shape and surrounded the β-phase.

In Comparative example 1, since the cooling speed of the casting was slow, the crystal grain size was great, namely 120 μm. Thus, a surface layer having a low Li concentration was not formed. The degree of orientation in the (110) plane of the β-phase was low, namely 41.5%.

As described above, in the Mg—Li alloy member according to the present disclosure, in which the degree of orientation in a (110) plane of a β-phase is more than or equal to 70%, the Li concentration of a surface layer of the base material, i.e., the Mg—Li alloy, with the average grain size of less than 50 μm is lower than the Li concentration of the inside of the base material. Thus, the alloy member is more excellent in corrosion resistance than a conventionally known alloy member.

Example 6

First, a cylindrical billet of an Mg—Li alloy as an alloy raw material was prepared. The Mg—Li alloy was Ares (composition: Mg-9% Li-1% Zn-4% Al, manufactured by Amli Materials Technology Co., Ltd.). As the sizes of the cylinder, the diameter of the bottom surface of the cylinder was 90 mm, and the length of the cylinder was 300 mm. Using the die-cast molding apparatus 200 illustrated in FIG. 3 , the cylindrical billet was melted at 610° C., and the melted alloy raw material was forced into the metal mold 205 at an injection speed of 5000 cm³/seconds. The temperature of the metal mold 205 was 150° C., and the melted alloy raw material was solidified at a cooling speed of 500° C./seconds to obtain a die-cast molded base material. The shape of the obtained base material was a square 50 mm on each side and had a thickness of 3 mm (a surface area of 56 cm²).

Next, using the anodization apparatus 309 illustrated in FIG. 3 , a surface layer and an anticorrosive film were formed. Specifically, the base material was connected to the conduction holding jig 308 prepared using AZ31 material to form an anode electrode using the base material of the circular ring shape and the conduction holding jig 308. The cathode electrode 306 was made of carbon. The electrolyte solution 302 was a neutral ammonium fluoride aqueous solution (pH=7.0) having a concentration of 450 g/L. The cathode electrode 306 and the anode electrode were placed in the neutral ammonium fluoride aqueous solution. Next, a voltage was applied between the cathode electrode 306 and the anode electrode. The temperature of the electrolyte solution 302 was controlled to be 20° C.±1° C. The current value of the power supply 305 was set to 0.56 A, the integral value of the current (the coulomb amount) after the voltage was applied was monitored, and the coulomb amount was controlled to be 682 C.

Coating was performed on the obtained base material. In the coating, Panuco SMG manufactured by Musashi Paint Co., Ltd., which was a one-component baking primer, was used as a primer layer. The film thickness when the base material was dried was 15 and the drying conditions were 160° C. and 20 minutes. In finishing coating, coating was performed using Armor Top manufactured by Musashi Paint Co., Ltd., which was a one-component acrylic resin coating material, under standard recommended conditions. The film thickness when the base material was dried was 15 and the drying conditions were 160° C. and 20 minutes. That is, the coating film includes a cured product of a resin.

An alloy member in Example 6 was obtained by the above steps.

Example 7

In Example 7, the current value of the anodization step was set to 1.4 A. An alloy member in example 7 was obtained by steps similar to those in Example 6 except for the difference in a current value.

Example 8

In Example 8, the current value of the anodization step was set to 2.8 A. An alloy member in Example 8 was obtained by steps similar to those in Example 6 except for the difference in a current value.

Example 9

In example 9, the current value of the anodization step was set to 4.2 A. An alloy member in Example 9 was obtained by steps similar to those in Example 6 except for the difference in a current value.

Example 10

In Example 10, the current value of the anodization step was set to 5.6 A. An alloy member in Example 10 was obtained by steps similar to those in Example 6 except for the difference in a current value.

Example 11

In Example 11, the current value of the anodization step was set to 0.56 A. Further, the coulomb amount was controlled to be 1022.9 C. An alloy member in Example 11 was obtained by steps similar to those in Example 6 except for the differences in a current value and the coulomb amount.

Example 12

In Example 12, the current value of the anodization step was set to 1.4 A. An alloy member in Example 12 was obtained by steps similar to those in Example 11 except for the difference in a current value.

Example 13

In Example 13, the current value of the anodization step was set to 2.8 A. An alloy member in Example 13 was obtained by steps similar to those in Example 11 except for a current value.

Example 14

In example 14, the current value of the anodization step was set to 4.2 A. An alloy member in Example 14 was obtained by steps similar to those in Example 11 except for a current value.

[Evaluation of Alloy Member]

Next, evaluation methods performed on Examples 6 to 14 and results of the evaluation are described.

First, in Examples 6 to 14, the average grain size was less than or equal to 50 μm, and the degree of orientation in the (110) plane of the β-phase was more than or equal to 70%.

(Measurement of Surface Roughness)

The surface roughness was measured using stylus profiler Alpha-Step D-600 manufactured by KLA-Tencor. The measurement was made with a scan width of 5 mm and a needle pressure of 1 mg. The arithmetic average surface roughness Ra [μm] and the maximum roughness Rz [μm] were read from the measurement result.

(Evaluation of Adhesiveness)

A crosscut test was performed. A 100-square grid test method was used with a cut interval of 1 mm. As determination criteria, A indicated that none of the squares peeled off, B indicated small peeling off corresponding to less than 10% of the coating film at intersections of cuts, and C indicated peeling off corresponding to 10% or more of the coating film.

(Evaluation of External Appearance)

The surface of the coating film was visually observed and evaluated. A product in which the entire surface of the surface of the coating film was even and uniform was ranked A. A product in which an uneven portion such as partial film unevenness or a difference in level was observed was ranked B.

The results of the above measurements and evaluations are summarized in table 2.

TABLE 2 Film thickness Current of surface Coulomb Film formation density Current layer amount Ra Rz External time [A/100 cm²] [A] [μm] [C] [μm] [μm] Adhesiveness appearance [min] Example 6 1 0.56 20 682 0.63 11.25 A A 20.3 Example 7 2.5 1.4 20 682 0.19 1.7 A A 8.12 Example 8 5 2.8 20 682 0.19 1.88 A A 4.06 Example 9 7.5 4.2 20 682 0.19 2.25 A A 2.71 Example 10 10 5.6 20 682 0.19 3.64 A A 2.03 Example 11 1 0.56 30 1022.9 0.87 10.97 A A 30.44 Example 12 2.5 1.4 30 1022.9 0.35 10.6 A A 12.18 Example 13 5 2.8 30 1022.9 0.25 3.3 A A 6.09 Example 14 7.5 4.2 30 1022.9 0.19 2.1 A A 4.06

From the results in table 2, it is understood that an alloy member with more than or equal to 0.19 μm of an average surface roughness Ra and more than or equal to 1 μm of a maximum roughness Rz is excellent in the adhesiveness and the external appearance of the coating film. That is, with respect to an alloy member in which the degree of orientation in a (110) plane of a β-phase is more than or equal to 70% or more, and the Li concentration of a surface layer of a base material, i.e., the Mg—Li alloy, with the average grain size of less than or equal to 50 μm is lower than the Li concentration of the inside of the base material, the average surface roughness Ra is set to more than or equal to 0.19 μm, and the maximum roughness Rz is set to more than or equal to 1 μm or more, whereby it is possible to make the adhesiveness and the external appearance of a coating film excellent.

The present disclosure is not limited to the above exemplary embodiments, and can be modified in many ways in the technical idea of the present disclosure. The effects described in the exemplary embodiments are merely a list of the most suitable effects provided by the present disclosure, and the effects of the present disclosure are not limited to those described in the exemplary embodiments.

While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Applications No. 2022-030264, filed Feb. 28, 2022, and No. 2023-005220, filed Jan. 17, 2023, which are hereby incorporated by reference herein in their entirety. 

What is claimed is:
 1. An alloy member comprising: a base material that includes a surface layer and is a Mg—Li alloy having an α-phase and a β-phase, wherein an anticorrosive film is able to be formed on the surface layer, wherein a degree of orientation in a (110) plane of the β-phase of the Mg—Li alloy is more than or equal to 70 percent (%), wherein an average grain size of the Mg—Li alloy is less than or equal to 50 micrometres (μm), and wherein a Li concentration of the surface layer is lower than a Li concentration of an inside of the base material.
 2. The alloy member according to claim 1, wherein a thickness of the surface layer is more than or equal to 10 μm.
 3. The alloy member according to claim 1, wherein a thickness of the surface layer is more than or equal to 30 μm.
 4. The alloy member according to claim 1, wherein a crystal shape of the α-phase of the Mg—Li alloy is a needle shape.
 5. The alloy member according to claim 4, wherein an average grain size in the α-phase of the Mg—Li alloy is less than or equal to 30 μm.
 6. The alloy member according to claim 1, further comprising: a Li compound, wherein after a lapse of two hours from cutting of the alloy member in a lamination direction, the Li compound is deposited from the base material.
 7. The alloy member according to claim 6, wherein the Li compound is at least one of lithium carbonate or lithium oxide.
 8. The alloy member according to claim 6, wherein a Li compound deposited from the surface layer is less than the Li compound deposited from the base material.
 9. The alloy member according to claim 1, further comprising: an anticorrosive film formed on the surface layer, wherein the anticorrosive film includes an inorganic fluoride.
 10. The alloy member according to claim 9, wherein the inorganic fluoride comprises magnesium fluoride (MgF₂), the proportion of the magnesium fluoride (MgF₂) of the inorganic fluoride is more than or equal to 90% By volume.
 11. The alloy member according to claim 9, wherein a thickness of the anticorrosive film is more than or equal to 2 μm.
 12. The alloy member according to claim 1, wherein the Mg—Li alloy has a Li content of more than or equal to 5% by mass and less than or equal to 11% by mass.
 13. The alloy member according to claim 1, wherein the Mg—Li alloy further contains one or more elements selected from the group consisting of aluminum (Al), zinc (Zn), manganese (Mn), silicon (Si), calcium (Ca), germanium (Ge), and beryllium (Be), and wherein a content of a sum of the one or more elements is less than or equal to 10% by mass.
 14. The alloy member according to claim 13, wherein the content of Al is less than or equal to 10% by mass, wherein the content of Zn is less than or equal to 3% by mass, wherein the content of Mn is less than or equal to 0.3% by mass, wherein the content of Si is less than or equal to 0.2% by mass, wherein the content of Ca is less than or equal to 1.0% by mass, wherein the content of Ge is less than or equal to 1% by mass, and wherein the content of Be is less than or equal to 3% by mass.
 15. The alloy member according to claim 9, wherein a surface of the anticorrosive film on a side opposite to a surface which is in contact with the surface layer has an average surface roughness Ra of more than or equal to 0.19 μm and less than or equal to 0.9 μm and a maximum roughness Rz of less than or equal to 15 μm.
 16. The alloy member according to claim 15, wherein the anticorrosive film has a porous structure.
 17. An apparatus comprising: a housing; and a component provided in the housing, wherein the housing includes the alloy member according claim
 1. 18. A method for manufacturing an alloy member, comprising: preparing a base material that is molded using die-cast molding and is an Mg—Li alloy having an α-phase and a β-phase; and forming a surface layer on the base material by performing an anodization process on the base material to obtain the surface layer having a Li concentration lower than a Li concentration of inside of the base material.
 19. The method for manufacturing the alloy member according to claim 18, wherein in the forming, the surface layer and an anticorrosive film on the surface layer are formed.
 20. The method for manufacturing the alloy member according to claim 18, wherein in the preparing, a molten alloy raw material is die-cast molded under application of pressure to obtain the base material of the Mg—Li alloy.
 21. The method for manufacturing the alloy member according to claim 18, wherein the forming includes placing a base material as a cathode and the base material of the Mg—Li alloy as an anode in a neutral ammonium fluoride aqueous solution, and applying a voltage between the anode and the cathode.
 22. The method for manufacturing the alloy member according to claim 18, further comprising heating the base material between the preparing and the forming. 